Floating offshore drilling vessels utilize an undersea riser system with a fixed length which extends from the surface to the sea floor. A telescopic joint at the upper end of the riser is used to compensate for swells in the open sea which vary the vertical distance between the drilling vessel and the sea floor. Tensioners extend from the vessel to the riser to hold it in tension. The tensioners include a collar or ring which surrounds and supports the riser at the telescopic joint. Tension cables or cylinders extend from the support ring to the vessel. The tension cables maintain tension and compensate for vertical movement of the vessel relative to the riser.
At times, the drilling vessel must be rotated to compensate for changing surface conditions, such as changes in the current or wind, in order to maintain the drilling vessel in position over the drilling site. During such rotations, the tensioners and supporting ring will rotate with the vessel relative to the telescopic joint. The riser system must be kept under tension during the rotation. A bearing is located between the support ring and the telescopic joint to accommodate the rotation. Although various bearings have been designed for telescoping joints, an improved bearing which better facilitates the rotation of undersea telescopic joints while maintaining high tension capacities is needed.